This section is intended to provide information relevant to understanding various technologies described herein. As the section's title implies, this is a discussion of related art that should in no way imply that it is prior art. Generally, related art may or may not be considered prior art. It should therefore be understood that any statement in this section should be read in this light, and not as any admission of prior art.
Relaxation oscillators are known in the art. FIG. 1A shows a conventional relaxation oscillator scheme 100A that uses a Schmitt inverter 110A to serve as a high gain hysteretic comparator, and as known, VIL, VIH (Voltage Input Low and Voltage Input High) of the Schmitt inverter 110A are typically used to set trip points. However, VIL/VIH may vary significantly with PVT (Process, Voltage, and Temperature), and hence, the conventional oscillator is less stable.
FIG. 1B shows another conventional relaxation oscillator scheme 100B that uses a fixed reference voltage Vref and a precision comparator 110B. In some cases, use of a low power comparator may result in significant delay that may affect oscillator stability. Thus, the scheme 100B may employ a relatively higher power design with use of the precision comparator 110B and a PVT independent reference generator 112. In this instance, some form of feedback FB may be employed via a feedback transistor T to correct the fixed reference voltage Vref or tune the precision comparator 110B so as to improve frequency stability. However, the fixed reference voltage Vref is non-ideal and does not typically perform well by design for stability when the supply voltage Vdd varies. Therefore, the scheme 100B may further use the feedback FB to compensate for variations in the reference voltage Vref so as to achieve better stability.
Another scheme (not shown) may refer to a differential resistor-capacitor (RC) network based relaxation oscillator that may be used to circumvent voltage dependence in a correct-by-design fashion. In some cases, the supply voltage (Vdd) is differentially sampled to cancel out variations. Reference generators are typically avoided by using a comparator's virtual ground as a reference to set a trip point. However, in practice, the comparator's virtual ground may move away from an ideal zero due to internal offsets, and thus, chopping may be used to average out any impact of offset to thereby improve stability. However, in this scheme, using differential sampling, a high power comparator, and a ring-oscillator increases power consumption, which should be avoided.